1. Field of the Invention
The present invention relates to a method of producing a single crystal by growing from a melt contained in a metallic container, such as a crucible, made of a metal such as platinum or platinum-based alloys in oxygen, air or an inert atmosphere.
2. Description of Related Art
Bismuth (Bi)-substituted garnet single crystals suitable for magneto-optical devices such as a photo-isolator, photo-circulator and photo-switch which utilize the Faraday effect are generally grown by a liquid phase epitaxial (hereinafter referred to as "LPE") process. The photo-isolator is used for cutting off a reflecting-returning light from optical elements such as connectors and switches and for stably oscillating a semiconductor laser. The miniaturization of the photo-isolator has been rapidly made with increase in demands. For the miniaturization, it is essential to miniaturize the Faraday rotor which is a main part of the photo-isolator. The Faraday rotor has an action to rotate an incident-light polarizing plane by a given quantity (for example, 45.degree.) and is needed to have a given length for the rotation. This length is in proportion to a Faraday rotation factor, and further miniaturization of the Faraday rotor requires to select a material having a higher Faraday rotation factor.
As the material high in the Faraday rotation factor, a so-called Bi-substituted magnetic garnet in the form of solid solution of Bi has been known, for example, in Japanese Patent Kokai (Laid-Open) No. 64-27212, and the Faraday rotation factor of this material increases in proportion to the amount of Bi substituted (see "Thin Solid Films", 114 (1984), pages 69-107). However, since the segregation coefficient of Bi for a garnet crystal is very small, it is very difficult to increase the substituted amount of Bi.
For substitution of Bi in a large amount in the LPE process, there have been proposed optimization of a component system and a composition of melt and optimization of LPE conditions (increase of a supercooling degree: saturation temperature--film growing temperature and lowering of a film growing temperature).